Usually if you just let it sit, it could take a couple of weeks.
What you want to do is wait till you see the Bacteria bloom. Your water will turn foggy and then clear up after a day or so.
That's a good indicator that your tank is cycled.
You can also use regular ammonia, 1 cocktail shrimp, or substrate and fake plants from an already established tank to jump start the cycle.
There are also certain chemicals you can use to cycle it as well.
I usually do a "fish in" cycle when I'm dealing with hardier fish that I know will make it. (Bettas being one of them.) Some people don't like this method cause it stresses the fish, but I've never lost a fish because of it.
Seachem makes a product called Stability which is supposed to be the best thing to use to jump start a cycle.
Seachem Stability sold on Amazon.
About Seachem Stability.